1. Field of the Invention
This invention relates to submersible, fluid-powered pumps, and more particularly to compact, small diameter pumps useful for obtaining liquid samples from deep subterranean locations via a borehole into which the pump is lowered.
2. Brief Description of the Prior Art
A number of fluid-powered pumps have been heretofore developed which utilize some type of small pilot valve of the spool type. In some of these, the pump is double-acting and includes pump pistons at opposite ends of the pump housing which alternately draw in and discharge a fluid to be pumped. Fluid-powered pumps of this general type include submersible pumps of a type adapted for use in oil wells. Examples of these types of pumps are those illustrated in Charles English U.S. Pat. Nos. 3,135,210; 3,336,941; 3,109,379; 3,024,733; 2,989,005 and 2,983,227.
Another design of pump which utilizes a spool type pilot valve to control the movements of a pair of pump pistons is that which is shown in Netherlands Pat. No. 41635. This patent depicts a fluid pump-motor arrangement in which a pair of main pistons are interconnected for mutual reciprocation, with control of their movement effected by a spool-type pilot valve which periodically shifts a spool-type distribution valve which directs power fluid to one of the cylinders in which the two main pistons are located, and concurrently exhausts spent power fluid from the other of the two main piston cylinders.
I have previously constructed a small diameter piston type pump containing an automatic cycle device and intended for expeditiously obtaining subterranean fluid samples. These pumps were utilized by the U.S. Geological Survey for this purpose. The pump was limited, however, in the operating pressure of the power fluid used to drive the pump, and was limited in the depth from which the fluid sample could be pumped.
These early pumps which I conceived and constructed had a pump housing diameter of 1.8 inches and an overall assembled length of 30 inches and weighed about 12 pounds. The prior pump, however, was difficult to start when it was installed at the end of 1600 feet of tubing bundle required to convey the power fluid to the pump. It contained an automatic cycling device which tended to stall or center when the pump was shut down. When the automatic cycling device was centered, a complicated procedure was then required to start the pump by relocation of the cycling device.
My prior pump was also less than optimum in that several small diameter external tubes or parts were required for construction of that pump, and it was therefore necessary to place a protective sleeve around the external tubes to shield the entire pump from damaging contact, and snagging in the borehole into which it was lowered. Moreover, the types of parts utilized in my earlier pump did not permit interchange of those parts from one pump to another, and therefore field replacement of some of the parts was impossible.